AIR-GAP FLUX DISTRIBUTION 287 



generated by the cutting of the end flux, and the component 

 to overcome the ohmic resistance of the windings. Now produce 

 PE g to Eg so that E g E f g represents the voltage that would be 

 developed by the slot flux if this were cut by the conductors. 

 OE'g, which may be called the apparent developed voltage, is 

 then the electromotive force that would have been developed in 

 the armature windings if the slot flux had actually entered the 

 core instead of being diverted from tooth to tooth by the action 

 of the current in the conductors. It is therefore also a measure 

 of the total flux passing through the air gap into the armature 

 teeth, and the magnetizing ampere-turns necessary to produce 

 this flux would, on open circuit, actually develop this electro- 

 motive force in the armature. Thus when the resultant mag- 

 netomotive force in the magnetic circuit is such that E' a volts 

 would be developed on open circuit, the terminal voltage under 



1 

 FIG. 114. Vector diagram of alternator operating at zero power factor. 



the assumed load conditions would be E*. It is usual, when the 

 power factor is zero, to consider this loss of pressure as equal to 

 the total reactive drop (E' P) because, owing to the relative 

 smallness of PE t and the fact that its direction is such as to 

 have little effect on the pressure drop, the error introduced by 

 this assumption is negligible. 



The length of the vector E g E' g in Fig. 114 can be calculated 

 from the known slot flux & ea as given by formula (104) of the 

 preceding article. If < a is the flux per pole actually cut by the 

 conductors, the total flux per pole in the air gap under load con- 

 ditions will be < = <l> a + 2<3> es . 



This total flux, if actually cut by the armature conductors, 

 would generate the electromotive force referred to as the "ap- 

 parent" developed voltage, and represented by OE' g in Fig. 114. 



The flux 2$ ea maxwells is the portion of the total air-gap flux 

 which, under load conditions, is no longer cut by the armature 



